Electrochemical impedance spectroscopy detect time

Noticeable progress has been made in recent years in the application of electrochemical impedance spectroscopy to biosensors. Compared to potentiometric detection, it requires a more complex electrode arrangement (three electrodes) and a more demanding detection circuit (potentiostat). In addition, the signal decreases with the electrode area and the measurements are taken over a range of frequencies. It is likely that both techniques are used in the future for different applications. For instance, potentiometric detection is particularly suitable for real-time detection, while EIS offers information for both charged and uncharged species. 

Electrochemical impedance spectroscopy is extensively employed for the investigation of SAMs because the broad range of frequencies covered by this technique (usually from 10 to 10 Hz) may allow processes with different relaxation times taking place within the electrified interphase to be detected and sorted out. Unfortunately, the various relaxation times often differ by less than 2 orders of magnitude, thus requiring a certain amount of arbitrariness and of physical intuition for their separation. In fact, it is well known that the same impedance spectrum can often be equally well fitted to different equivalent circuits, which are consequently ascribed to different relaxation processes. Impedance spectra are frequently reported on a Y /co versus Y"/co plot, where Y and Y" are the in-phase and quadrature components of the electrochemical admittance and co is the angular frequency. This plot is particularly suitable for representing a series RC network. Thus, a series connection of R and C yields... 

Chai, C. and Takhistov, P. (2010) Label-free toxin detection by means of time-resolved electrochemical impedance spectroscopy Sensors, 10, 655-669. 

---